Interannual variability of the ecosystem CO₂ fluxes at paludified spruce forest and ombrotrophic bog in southern taiga

Abstract. Climate warming in high latitudes impacts CO₂ sequestration of northern peatlands through the changes in both production and decomposition processes. The response of the net CO₂ fluxes between ecosystems and the atmosphere to the climate change and weather anomalies can vary across the forest and non-forest peatlands. To better understand the differences in CO₂ dynamics at forest and non-forest boreal peatlands induced by changes in environmental conditions the estimates of interannual variability of the net ecosystem exchange (NEE), total ecosystem respiration (TER) and gross primary production (GPP) was obtained at two widespread peatland ecosystems – paludified spruce forest and adjacent ombrotrophic bog in the southern taiga of west Russia using 6-year of paired eddy covariance flux measurements. The period of measurements (2015–2020) was characterized by both positive and negative annual and growing season air temperature and precipitation anomalies. Flux measurements showed that in spite of the lower growing season TER (332…339 gC∙m⁻²) and GPP (442…464 gC∙m⁻²) rates the bog had a lower NEE (−132…−108) than the forest excepting the warmest and the wettest year of the period and was a sink of atmospheric CO₂ in the selected years while the forest was a CO₂ sink or source between years depending on the environmental conditions. Growing season NEE at the forest site was between −142 and 28 gC∙m⁻², TER between 1135 and 1366 gC∙m⁻² and GPP between 1207 and 1462 gC∙m⁻². Annual NEE at the forest was between −62 and 145 gC∙m⁻², TER between 1429 and 1652 gC∙m⁻² and GPP between 1345 and 1566 gC∙m⁻² respectively. Anomalously warm winter with sparse and thin snow cover lead to the increased GPP as well as lower NEE in early spring at forest and to the increased spring TER at the bog. Also, the shifting of the compensation point to the earlier dates at the forest and to the later dates at the bog following the warmest winter of the period was detected. This study suggest that the warming in winter can increase CO₂ uptake of the paludified spruce forests of southern taiga in non-growing season.